Process for producing metal oxide catalyst

ABSTRACT

The invention relates to a process for producing a metal oxide catalyst capable of producing acrylic acid, acrylonitrile or the like in one stage by catalytic oxidation reaction of propane in a high yield. 
     The invention is characterized by using one obtained by finely ground metallic Te or metallic Sb in water or an organic solvent as a raw material for the production of an oxide catalyst made of metal elements Mo—V—Nb—Te or metal elements Mo—V—Nb—Sb. The powder of the metallic Te or metallic Sb obtained by grinding preferably has a mode size of not more than 20 μm. By using the metal oxide obtained by the invention as a catalyst, it is possible to produce acrylic acid in a high yield of 35% or more from propane by a one-stage oxidation reaction.

TECHNICAL FIELD

The present invention relates to a process for producing a metal oxidecatalyst which is used in the production of acrylic acid by vapor phasecatalytic oxidation of propane, the production of acrylonitrile byammoxidation of propane and the like.

BACKGROUND ART

In general, acrylic acid is produced by a two-stage oxidation reactionof undergoing catalytic reaction of propylene with oxygen in thepresence of a catalyst to produce acrlolein and undergoing catalyticreaction of the resulting acrlolein with oxygen.

On the other hand, in the recent years, due to a price differencebetween propane and propylene and for the purpose of overcoming problemssuch as complexity in process involving the two-stage oxidation, aprocess for producing acrylic acid in one stage by using propane as astarting material is studied, and there have been made a number ofproposals with respect to catalysts to be used therefor. Asrepresentative examples thereof, there are enumerated catalysts made ofa composite metal oxide such as [V, P, Te] bases, [Mo, Te, V, Nb] bases,and [Mo, Sb, V, Nb] bases.

Recently, there have been filed some applications for patent withrespect to improvements of the foregoing metal oxide catalysts. That is,JP-A-10-137585 discloses a process for producing a catalyst by mixing areaction aqueous solution obtained by allowing a molybdenum compound, avanadium compound and an antimony compound to react in an aqueous mediumat 70° C. or higher with a niobium compound, evaporating to dryness theresulting mixture, and further calcining it at a high temperature.

JP-A-10-230164 describes that in heat treating the respective metalcompounds in the aqueous medium described in the foregoing patentdocument, a gas containing molecular oxygen is introduced into theaqueous medium and that when the catalyst as produced in this process isused for vapor phase oxidation reaction of propane, the yield of acrylicacid is further enhanced.

Also, JP-A-11-285636 describes a method for adding hydrogen peroxide toa reaction liquid of the respective metal compounds under heating andreaction or a reaction liquid thereof after the reaction in the aqueousmedium as described in the foregoing JP-A-10-137585 and JP-A-10-230164.

However, even in the case of using the catalysts as described in theforegoing patent documents, the yield of acrylic acid in a one-stageoxidation reaction of propane does not reach a practical level requiredin the acrylic acid production.

JP-A-11-226408 discloses a method for allowing a metal powder to reactwith an oxometalate of other element and using a reaction liquid havingthe metal powder substantially dissolved therein as a raw material inthe production of a catalyst. In this method, it is described that forthe purpose of accelerating the reaction of the metal powder having asmall dissolution rate, heating is carried out over a long period oftime and that an oxidizing agent is added. However, JP-A-11-226408 doesnot provide any description with respect to a grinding treatment of themetal powder.

DISCLOSURE OF THE INVENTION

In order to obtain a catalyst capable of producing acrylic acid,acrylonitrile or the like in one stage by catalytic oxidation reactionof propane in a high yield, the present inventors made extensive andintensive investigations. As a result, it has been found that theforegoing problems can be solved by using one prepared by finelygrinding Te or Sb as a raw material in the production of a metal oxidecatalyst in water or an organic solvent, leading to accomplishment ofthe invention. Accordingly, an object of the invention is to provide aprocess for producing a metal oxide catalyst upon which the foregoingproblems are solved.

The invention of achieving the foregoing object is concerned with aprocess for producing a metal oxide catalyst represented by thefollowing composition formula, which is characterized by using, as a rawmaterial, a fine particle dispersion of metallic Te or Sb obtained bygrinding the following metallic Te or Sb in the presence of water or anorganic solvent not containing any of Mo⁶⁺ compounds and V⁵⁺ compounds.MoV_(i)A_(j)B_(k)O_(y)  Composition formula:(In the formula, A is Te or Sb; and B is at least one element selectedfrom the group consisting of Nb, Ta, W, Ti, Zr, Re, Fe, Ni, Co, Sn, Tl,Cu, rare earth elements, and alkali metal elements. i and j are eachfrom 0.01 to 1.5, and j/i is from 0.3 to 1.0; k is from 0.001 to 3.0;and y is the number to be determined by the oxidized state of otherelements.)

Also, the invention is concerned with a process for producing a metaloxide catalyst represented by the following composition formula, whichis characterized by employing a process comprising the following step(1), step (2), step (3) and step (4).

Step (1): A step in which the following metal A is ground in thepresence of water or an organic solvent not containing any of Mo⁶⁺compounds and V⁵⁺ compounds;

Step (2): A step in which in the case where an aqueous dispersion hasbeen obtained in the foregoing step (1), an aqueous dispersion resultingfrom adding an Mo⁶⁺ compound and a V⁵⁺ compound to the subject aqueousdispersion is heated at 60° C. or higher for at least 10 minutes, or inthe case where an organic solvent dispersion has been obtained in thestep (1), an aqueous dispersion resulting from adding an Mo⁶⁺ compoundand a V⁵⁺ compound to an aqueous dispersion obtained by substituting theorganic solvent with water is heated at 60° C. or higher for at least 10minutes;

Step (3): A step in which a compound containing the following metal B isadded to a reaction liquid obtained in the foregoing step (2); and

Step (4): A step in which a dried material obtained by evaporating todryness a mixed liquid obtained in the foregoing step (3) is dried andfurther calcined.MoV_(i)A_(j)B_(k)O_(y)  Composition formula:(In the formula, A is Te or Sb; and B is at least one element selectedfrom the group consisting of Nb, Ta, W, Ti, Zr, Re, Fe, Ni, Co, Sn, Tl,Cu, rare earth elements, and alkali metal elements. i and j are eachfrom 0.01 to 1.5, and j/i is from 0.3 to 1.0; k is from 0.001 to 3.0;and y is the number to be determined by the oxidized state of otherelements.)

Further, the invention is concerned with a process for producing acrylicacid or acrylonitrile, which is characterized by subjecting propane tooxidation by vapor phase catalytic reaction or ammoxidation in thepresence of the metal oxide catalyst as produced by the foregoingprocesses.

BEST MODE FOR CARRYING OUT THE INVENTION

The process for producing a metal oxide catalyst of the invention willbe hereunder described while dividing into steps (1) to (4).

(Step 1)

In the process for producing a metal oxide catalyst of the invention, ametal A as a raw material of the catalyst, that is, metallic Te ormetallic Sb, is ground and dispersed. The raw material metal A ispreferably one in a particulate form. Specifically, one having aparticle size of not more than 200 μm is preferable because it is easilyground.

The grinding of the metal A is carried out in the presence of water oran organic solvent. Water or an organic solvent which does not containany of Mo⁶⁺ compounds and V⁵⁺ compounds (hereinafter sometimes referredto as “specific metal compounds”) is used. The case where the metal A isground in water or an organic solvent containing these specific metalcompounds is already filed as an application for patent (Japanese PatentApplication No. 2002-360492).

Though the organic solvent which is used during grinding is notparticularly limited, organic solvents which are liquid at the ambienttemperature and can be easily removed in a post step are preferable.Specifically, alcohols such as methanol, ethanol, and propanol, andhydrocarbons such as hexane, cyclohexane, and toluene are preferable.When water or the organic solvent is co-present at the time of grinding,an increase of the surface energy accompanying the grinding is relieved,and grinding efficiency is enhanced.

With respect to a mixing proportion of water or the organic solvent tothe metal A at the time of grinding, water or the organic solvent ispreferably used in an amount of from 10 to 1,000 parts by mass, and morepreferably from-30 to 300 parts by mass based on 100 parts by mass ofthe metal A. When the mixing proportion of water or the organic solventto the metal A is less than 10 parts by mass, the metal A adheres to agrinding vessel so that the grinding becomes difficult. Also, when itexceeds 1,000 parts by mass, the solvent absorbs the impact during thegrinding so that grinding efficiency is lowered.

For a grinding machine, a mode by which grinding is conducted by drivingthe vessel containing the material to be ground to roll is preferable.Specifically, there are enumerated a ball mill, a vibration mill, aplanetary ball mill, and the like. A grinding time is suitably from 0.5to 24 hours.

By the foregoing grinding treatment, a dispersion having the metal Adispersed in water or an organic solvent is obtained. The metal A powderin the dispersion preferably has a mode size (a particle size regionwhere when a particle size distribution of the powder is measured, thelargest amount of powders are contained) of not more than 20 μm, andmore preferably from 15 to 0.6 μm. The mode size of the metal A becomessmaller by a heating step as described later, and it is preferable thatthe particle size of the metal A powder after that heating step becomesnot more than 0.1 μm. On the other hand, in the case where the mode sizeof the metal A powder after grinding exceeds 20 μm, the metal A powderhaving a mode size of 0.5 μm or more remains even after completion ofthe heating step, thereby lowering the performance of the metal oxidecatalyst as ultimately produced.

In the foregoing grinding treatment, it is preferred to further addaqueous solution of hydrogen peroxide to water or the organic solvent.With the presence of aqueous solution of hydrogen peroxide, theperformance of the resulting metal oxide catalyst is more enhanced.Though the details of the mechanism for the enhanced catalyticperformance generated by the addition of aqueous solution of hydrogenperoxide are not clarified yet at present, it is assumed that with thepresence of aqueous solution of hydrogen peroxide in water or theorganic solvent, dispersion of the metal A powder in the resultingdispersion is stabilized, the high dispersion state is kept withoutcausing sedimentation, and this gives preferable influences in theproduction of the metal oxide catalyst.

An addition amount of aqueous solution of hydrogen peroxide to be addedto water or the organic solvent is preferably from 0.1 to 3.0 moles, andmore preferably from 0.3 to 1.5 moles per mole of the metal A. When theaddition amount of hydrogen peroxide is less than 0.1 moles, theenhancement of the performance of the resulting metal oxide catalyst issmall, whereas when the addition amount of hydrogen peroxide exceeds 3.0moles, the metal A powder is completely dissolved in the heating step asdescribed later so that the performance of the resulting metal oxidecatalyst is lowered.

(Step 2)

In the case where an aqueous dispersion of the metal A has been obtainedin the foregoing step (1), an Mo⁶⁺ compound and a V⁵⁺ compound are addedto the subject aqueous dispersion.

In the case where an organic solvent dispersion of the metal A has beenobtained in the foregoing step (1), the organic solvent is substitutedwith water, and an Mo⁶⁺ compound and a V⁵⁺ compound are added to anaqueous dispersion of the metal A as obtained by the substitution.Examples of a method for substituting the organic solvent with waterinclude a method by distilling off the organic solvent from the organicsolvent dispersion in vacuo and a method by removing the organic solventwith a centrifugation operation and then redispersing the residue inwater. Incidentally, it is not necessary to completely remove theorganic solvent. In the case where the content of the organic solvent inthe aqueous dispersion is less than 3%, there is not substantiallygenerated a problem. When a water-soluble alcohol is used as the organicsolvent, an aqueous dispersion may be prepared by adding water to analcohol-containing dispersion.

Examples of the Mo⁶⁺ compound include ammonium molybdate, molybdenumoxide, and molybdic acid. Of these compounds, ammonium molybdate ispreferable because it is water-soluble. Also, as the V⁵⁺ compound,ammonium metavanadate, vanadium pentoxide, and the like are preferable.

The addition amount of each the Mo⁶⁺ compound and the V⁵⁺ compound isfrom 0.01 to 1.5 in terms of an atomic ratio of V and the metal A (i andj) based on Mo, and an atomic ratio of the metal A to V (j/i) is from0.3 to 1.0.

When the proportions of Mo, V and the metal A fall outside the foregoingranges, a metal oxide catalyst having an expected performance cannot beobtained.

Next, the aqueous dispersion having the Mo⁶⁺ compound and the V⁵⁺compound added thereto is subjected to heat treatment. For the purposeof improving the operability or other purpose, the aqueous dispersionmay be diluted by the addition of water as the need arises. With respectto the heating condition, the heating is carried out at 60° C. orhigher, and preferably at from 70 to 100° C. preferably for from 10minutes to 10 hours, and more preferably for from 30 minutes to 3 hours.It is preferred to stir the aqueous dispersion during heating.

By adding the Mo⁶⁺ compound and the V⁵⁺ compound to the aqueousdispersion of the ground metal A fine particle and heating the mixtureunder the foregoing condition, a deeply blue reaction liquid in whichthe metal A fine particle having a particle size of not more than 100 nmis stably dispersed is obtained.

When the heating temperature or heating time falls outside the foregoingrange, the metal A is liable to cause excessive reaction. As an exampleof the excessive reaction, in the case of using Te as the metal A,tellurium dioxide which is insoluble in water is formed, resulting in areduction of the performance of the resulting metal oxide catalyst.

(Step 3)

In the step (3), a compound containing a metal B is added to thereaction liquid as obtained via the foregoing steps (1) and (2). By thisaddition operation, a fine precipitate is formed in the reaction liquid.Though the reaction temperature is not particularly limited, thereaction temperature is usually at room temperature.

The metal B is at least one element selected from the group consistingof Nb, Ta, W, Ti, Zr, Re, Fe, Ni, Co, Sn, Tl, Cu, rare earth elements,and alkali metal elements.

Examples of the B-containing compound which can be used in the inventioninclude oxides, nitrates, carboxylates, oxometalates, and oxalates. Theinsoluble B-containing compound may be dispersed in water and providedfor use. In this case, by jointly using oxalic acid, etc., the compoundcan be dissolved in water.

An addition amount of the B-containing compound is an amount such thatwhen Mo is defined as 1, the metal B is from 0.001 to 3 in terms of anatomic ratio in the resulting metal oxide catalyst. In the subjectcatalyst, in the case where when Mo is defined as 1, the proportion ofthe metal B is less than 0.001, deterioration of the resulting catalystis liable to occur. On the other hand, in the case where it exceeds 3.0,the activity of the resulting catalyst becomes low, and the conversionof propane is inferior.

In the step (3), by adding ammonium nitrate and ammonia water togetherwith the B-containing compound to the reaction liquid as obtained viathe step (2), the catalytic performance of the resulting metal oxide isenhanced. With respect to preferred use amounts of ammonium nitrate andammonia water, the amount of ammonia water is an amount containing 0.4or more of ammonia in terms of a molar ratio to the metal B, and theamount of ammonium nitrate is an amount containing 2.0 or more of anitric acid ion in terms of a molar ratio to the metal B, respectively.

(Step 4)

In the step (4), the mixed liquid (slurry) as obtained via the foregoingstep (3) is evaporated to dryness, and the resulting dried material isdried and then calcined. For the sake of removing a large amount ofwater as contained, the foregoing mixed liquid can be dried by aconventionally known method such as evaporation to dryness and spraydrying. In the case of evaporation to dryness, though the water may beevaporated merely by heating, when a method for blowing an inert gassuch as nitrogen and air is employed, it is possible to efficientlyachieve evaporation to dryness. A temperature of the evaporation todryness is preferably in the range of from 50 to 130° C.

Next, the dried material as obtained by the foregoing operation is firstcalcined at a temperature of from 250 to 380° C., and preferably from280 to 330° C. for from 2 to 20 hours, and preferably from 3 to 10 hoursin the presence of oxygen. Thereafter, the resulting material is furthercalcined at a temperature of from 500 to 660° C., and preferably from570 to 620° C. for from 0.5 to 6 hours, and preferably from 1 to 3 hoursin the absence of oxygen.

In the invention, it is preferred to obtain a metal oxide catalystrepresented by the following composition formula by this two-stagecalcining.MoV_(i)A_(j)B_(k)O_(y)  Composition formula:

(In the formula, A is Te or Sb; and B is at least one element selectedfrom the group consisting of Nb, Ta, W, Ti, Zr, Re, Fe, Ni, Co, Sn, Tl,Cu, rare earth elements, and alkali metal elements. i and j are eachfrom 0.01 to 1.5, and j/i is from 0.3 to 1.0; k is from 0.001 to 3.0;and y is the number to be determined by the oxidized state of otherelements.)

Incidentally, the determination of the contents of metal elements in themetal oxide catalyst as obtained by the foregoing calcining can becarried out by fluorescent X-ray analysis.

The metal oxide catalyst as obtained by the foregoing method can be usedas it is. However, it is preferable that the metal oxide catalyst isground in an appropriate particle size, thereby increasing a surfacearea of the catalyst and then provided for use. As grinding methods, anymethod of a dry-type grinding method and a wet-type grinding method canbe employed.

Specific examples of a grinding device include a mortar and a ball mill.In the case of wet-type grinding, as grinding assistants, water,alcohols, and the like are enumerated.

In the case where the present catalyst is ground and used, its particlesize is preferably not more than 20 μm, and more preferably not morethan 5 μm.

Though the metal oxide catalyst can be used in a non-supported state, itcan also be used by supporting on a known carrier having an appropriateparticle size, such as silica, alumina, silica-alumina, and siliconcarbide. The supporting amount is not particularly limited but follows aconventional supporting amount.

Next, the vapor phase catalytic oxidation reaction method of propaneusing the metal oxide catalyst as produced by the foregoing productionprocess will be hereunder described.

Propane and oxygen as raw materials of the production of acrylic acidare introduced into a reactor charged with the foregoing metal oxidecatalyst and catalytically oxidized by the metal oxide catalyst, therebyproducing acrylic acid.

Propane and oxygen may be separately introduced into a reactor, the bothof which are then mixed within the reactor; and the both may be mixed inadvance and then introduced into a reactor. Examples of oxygen include apure oxygen gas and air, or a diluted gas thereof with nitrogen, steamor carbon dioxide. In the case where propane and air are used as rawmaterials, a use proportion of air to propane is preferably not morethan 30 times, and more preferably from 0.2 to 20 times in terms of avolume ratio. Though the unreacted raw material propane present in areaction gas to be discharged from an outlet of the reactor or propyleneas an intermediate can be used as a fuel as it is, the unreacted rawmaterial propane or propylene as an intermediate which has beenseparated from other components in the reaction gas can be returned intothe reactor and reused.

A reaction temperature is preferably from 300 to 600° C., and morepreferably from 350 to 500° C.

A space velocity (hereinafter referred to as “SV”) of the raw materialgas is suitably from 1,000 to 8,000 hr⁻¹. When the space velocity isless than 1,000 hr⁻¹, a space time yield of acrylic acid as the targetedcompound becomes low, whereas when it exceeds 8,000 hr⁻¹, the conversionis lowered.

The metal oxide catalyst as produced in the invention can also beapplied to ammoxidation of propane and can synthesize acrylonitrile in ahigh yield. The ammoxidation condition substantially follows theforegoing vapor catalytic oxidation condition of propane.

The invention will be more specifically described below with referenceto the Examples and Comparative Examples. Incidentally, in the followingExamples 1 to 7 and Comparative Examples 1 to 2, the respective rawmaterials were blended such that all of proportions of the respectivemetals constituting the resulting metal oxide catalysts became thefollowing values.Mo/V/A/Nb=1.0/0.3/0.18/0.08

1.5 mL (about 2.2 g) of the catalyst as produced in each Example wascharged in a 10-mmφ quartz-made reaction tube. The reaction tube washeated at 400° C., and a mixed gas containing 6.4% by volume of propane,9.6% by volume of oxygen, 36.1% by volume of nitrogen and 47.7% byvolume of steam was fed into the reaction tube at a space velocity of3,924hr⁻¹, thereby producing acrylic acid.

Respective components as formed in the reaction product were subjectedto composition analysis. By using the results of the compositionanalysis, a conversion of propane and a selectivity of acrylic acid (allof which are on a molar basis) were calculated according to thefollowing expressions, and the performance of the used catalyst wasevaluated from the values. The results are shown in Table 1. In Table 1,AA stands for acrylic acid; and P stands for propane.Conversion of propane (%)=100×[(Fed propane)−(Unreacted propane)]/(Fedpropane)Selectivity of acrylic acid (%)=100×(Formed acrylic acid)/[(Fedpropane)−(Unreacted propane)]Yield of acrylic acid (%)=(Conversion of propane)×(Selectivity ofacrylic acid)/100

EXAMPLE 1

In a ceramics-made pot for grinding having a volume of 500 mL, 2.01 g ofa metallic tellurium powder (a mean particle size: 150 μm) and 2.6 g ofdistilled water were charged and mixed, and 25 zirconia balls having asize of 10 mm (ZrO₂: 95%, density: 6.0 g/cm³) and 5 balls of the samematerial quality having a size of 20 mm were then charged therein. Theforegoing pot was placed on two rotary rolls and subjected to grindingtreatment by rotating at a rotational speed of 170 rpm for 24 hours.

A small amount of a sample was collected from an aqueous dispersionafter grinding treatment (hereinafter referred to as “dispersion a”),and the particle size distribution of the tellurium powder was measuredby using HORIBA, LA-500 Model, a laser diffraction type particle sizedistribution analyzer. A mode size representing a representativeparticle size was 2.0 μm. Incidentally, in the foregoing grinding step,a weight ratio of water to Te was 1.3.

Separately, in a 500-mL glass-made flask, 3.07 g of ammoniummetavanadate, 15.45 g of ammonium molybdate, and 50 mL of distilledwater were added and dissolved with stirring at the boiling temperatureof water. To the resulting solution, the foregoing dispersion a and 40 gof distilled water were added, and the mixture was refluxed at theboiling temperature of water for one hour while rotating at a rotationalspeed of 500 rpm by a stirring machine, thereby obtaining a deeply bluereaction liquid (hereafter referred to as “reaction liquid b”).

The flask having the foregoing reaction liquid b charged therein wascooled to 30° C. with ice water. On the other hand, 4.41 of oxalic acidand 1.16 g of niobic acid were dissolved in 70 mL of distilled water toprepare an aqueous solution of the ambient temperature, and this aqueoussolution was then added to the foregoing reaction liquid b. Theresulting mixed liquid was vigorously stirred for 10 minutes, and 2.5 gof ammonium nitrate was then mixed with this mixed liquid. Thereafter,the resulting mixture was heated for concentration and furtherevaporated to dryness at 120° C.

The resulting dried material was calcined in air at 300° C. for 5 hours.Thereafter, the resulting calcined material was further calcined at 600°C. for 2 hours in an inert atmosphere through which nitrogen was passed,thereby obtaining a metal oxide catalyst. The resulting catalyst wassubjected to tablet making and further pulverized into from 16 to 30meshes, and then used for production reaction of acrylic acid. Theresults are shown in Table 1.

EXAMPLE 2

A catalyst was prepared in the same manner as in Example 1, except thatthe amount of water to be used for the preparation of the dispersion awas changed to 5.0 g. A mass ratio of water to Te in grinding step was2.5. Incidentally, as a result of measurement of the particle sizedistribution of the metallic Te particle after grinding, the modeparticle size was found to be 2.6 μm.

By using the resulting catalyst, acrylic acid was produced under thesame condition as in Example 1. The results are shown in Table 1.

EXAMPLE 3

A catalyst was prepared in the same manner as in Example 1, except thatthe amount of water to be used for the preparation of the dispersion awas changed to 13.0 g. A mass ratio of water to Te in grinding step was6.5. Incidentally, as a result of measurement of the particle sizedistribution of the metallic Te particle after grinding, the modeparticle size was found to be 8.8 μm.

By using the resulting catalyst, acrylic acid was produced under thesame condition as in Example 1. The results are shown in Table 1.

EXAMPLE 4

A catalyst was prepared in the same operation as in Example 1, exceptthat 2.5 g of ethanol was used in place of the water as used in thepreparation of the dispersion a. A mass ratio of ethanol to Te ingrinding step was 1.3. Incidentally, the particle size distribution ofthe metallic Te particle after grinding was measured. The mode particlesize was found to be 3.2 μm.

By using the resulting catalyst, acrylic acid was produced under thesame condition as -in Example 1. The results are shown in Table 1.

EXAMPLE 5

A catalyst was produced in the same operation as in Example 1, exceptthat in the preparation of the dispersion a, a mixture of 0.5 g ofaqueous solution of hydrogen peroxide having a concentration of 35% bymass and 5.0 g of distilled water was supplemented. A molar ratio ofhydrogen peroxide to Te in grinding step was 0.33. The particle sizedistribution of the metallic Te particle after grinding was measured.The mode particle size was found to be 5.8 μm.

By using the resulting catalyst, acrylic acid was produced under thesame condition as in Example 1. The results are shown in Table 2.

EXAMPLE 6

A catalyst was produced in the same manner as in Example 1, except thatin the preparation of the dispersion a, a mixture of 1.57 g of aqueoussolution of hydrogen peroxide having a concentration of 35% by mass. and5.0 g of distilled water was supplemented. A molar ratio of hydrogenperoxide to Te in grinding step was 1.0. The particle size distributionof the metallic Te particle after grinding was measured. The modeparticle size was found to be 3.9 μm.

By using the resulting catalyst, acrylic acid was produced under thesame condition as in Example 1. The results are shown in Table 2.

EXAMPLE 7

A catalyst was produced in the same operation as in Example 1, exceptthat in the preparation of the dispersion a, a mixture of 3.14 g ofaqueous solution of hydrogen peroxide having a concentration of 35% bymass and 5.0 g of distilled water was supplemented. A molar ratio ofhydrogen peroxide to Te in grinding step was 2.0. The particle sizedistribution of the metallic Te particle after grinding was measured.The mode particle size was found to be 2.3 μm.

By using the resulting catalyst, acrylic acid was produced under thesame condition as in Example 1. The results are shown in Table 2.

EXAMPLE 8

A dispersion of Te was produced in the same operation as in Example 1,except that in the preparation of the dispersion a, not only the amountof the metallic Te powder was changed to 1.45 g, but also a mixture of1.13 g of aqueous solution of hydrogen peroxide having a concentrationof 35% by mass and 5.0 g of distilled water was supplemented. A molarratio of hydrogen peroxide to Te in grinding step was 1.0. The particlesize distribution of the metallic Te particle after grinding wasmeasured. The mode particle size was found to be 5.8 μm.

In a 500-mL glass-made flask, 2.66 g of ammonium metavanadate, 3.0 g ofammonium molybdate, and 50 mL of distilled water were added anddissolved with stirring at the boiling temperature of water. To theresulting solution, the foregoing metallic tellurium dispersion wasadded, and the mixture was subjected to heat treatment for one hour.12.45 g of ammonium molybdate was dissolved in the resulting reactionliquid, 1.4 g of 30% ammonia water was further dropped in the solution,and the reaction liquid then reached 60° C. after a lapse of severalminutes with stirring. On the other hand, 5.89 g of oxalic acid and 2.32g of niobic acid were dissolved in 160 mL of distilled water to preparean aqueous solution of the ambient temperature, and this aqueoussolution was added to the foregoing reaction liquid. After vigorouslystirring the resulting mixed liquid for 10 minutes, this mixed liquidwas mixed with 3.5 g of ammonium nitrate. Thereafter, the mixture washeated for concentration and further evaporated to dryness at 120° C. byusing a drying machine.

The resulting dried material was calcined in air at 320° C. for 1.5hours. The resulting catalyst precursor was calcined in the absence ofoxygen under the condition at 590° C. for 1.5 hours, thereby obtaining ametal oxide catalyst. This catalyst had a metal atomic ratio ofcomponents of Mo/V/Te/Nb of 1.0/0.25/0.13/0.16 (molar ratio).

The resulting catalyst was subjected to tablet making and furtherpulverized into from 16 to 30 meshes, and then used for productionreaction of acrylic acid. As a result, a conversion of propane was60.1%, a selectivity of acrylic acid was 80.5%, and a yield of acrylicacid was 48.45%, respectively.

COMPARATIVE EXAMPLE 1

To an aqueous dispersion of 2.01 g of an unground metallic Te particle(mean particle size: 150 μm) dispersed in 95 g of water, 15.45 g ofammonium molybdate and 3.07 g of ammonium metavanadate were added, andthe mixture was heated. After the heating, all of the same operations asin Example 1 were followed, thereby producing a catalyst. By using thiscatalyst, acrylic acid was produced under the same condition as inExample 1. The results are shown in Table 1.

COMPARATIVE EXAMPLE 2

The step (1) for grinding metallic Te was omitted, and 15.45 g ofammonium molybdate, 3.07 g of ammonium metavanadate, and 4.62 g oftelluric acid were directly heated and dissolved to obtain a reactionliquid b. After the heating, all of the same operations as in Example 1were followed, thereby producing a catalyst. By using this catalyst,acrylic acid was produced under the same condition as in Example 1. Theresults are shown in Table 1.

COMPARATIVE EXAMPLE 3

15.45 g of ammonium molybdate was dissolved in 70 g of distilled water,into which was then suspended 2.01 g of a metallic Te powder (meanparticle size: 150 μm) at room temperature. To this suspension, 4.7 g of35% by mass aqueous solution of hydrogen peroxide [hydrogen peroxide/Te:3.1 (molar ratio)] was added, and the mixture was heated at 70° C. withstirring. Following the heating, Te was dissolved so that the mixtureultimately became a colorless solution. To this solution, 3.07 g ofammonium metavanadate was added and dissolved, and the flask having thissolution charged therein was cooled to 30° C. with ice water.Separately, an aqueous solution of the ambient temperature of 4.41 g ofoxalic acid and 1.16 g of niobic acid dissolved in 70 mL of distilledwater was prepared and mixed with the foregoing solution cooled to 30°C.

After vigorously stirring the resulting mixed liquid for 10 minutes, 2.5g of ammonium nitrate was added to this mixed liquid and uniformlymixed. Thereafter, the mixture was heated for concentration and furtherevaporated to dryness at 120° C.

The resulting dried material was calcined in air at 300° C. for 5 hours.The resulting material was further calcined at 600° C. for 2 hours whilepassing nitrogen therethrough, thereby obtaining a catalyst. Thiscatalyst had an atomic ratio of components of Mo/V/Te/Nb of1.0/0.3/0.18/0.08. This catalyst was dried, subjected to tabletting, andfurther pulverized into from 16 to 30 meshes. By using the resultingcatalyst, acrylic acid was produced under the same condition as inExample 1. The results are shown in Table 1.

TABLE 1 Water/Te Conversion Selectivity Yield of (mass ratio) of P (%)of AA (%) AA (%) Example 1 1.3 40.0 74.5 34.3 Example 2 2.5 49.2 75.637.2 Example 3 6.5 47.9 74.8 35.8 Example 4 1.3 51.2 72.1 36.9Comparative Not ground 11.6 56.9 6.6 Example 1 Comparative Not ground29.6 57.9 17.1 Example 2 Comparative Not ground 37.8 76.1 28.2 Example 3

TABLE 2 Water/Te Conversion Selectivity Yield of (mass ratio) of P (%)of AA (%) AA (%) Example 5 0.33 54.3 74.9 40.7 Example 6 1.00 56.3 79.844.9 Example 7 2.00 52.1 78.7 41.0

INDUSTRIAL APPLICABILITY

According to the production process of the invention, since a fineparticle dispersion obtained by grinding metallic Te or Sb in thepresence of water or an organic solvent is used as a raw material in thecatalyst production, a metal oxide catalyst with high performance can beobtained with good reproducibility. By using this catalyst in theproduction of acrylic acid by vapor phase catalytic oxidation reactionof propane, it is possible to obtain acrylic acid in a high yield. Also,the present metal oxide catalyst can also be used for ammoxidation ofpropane.

1. A process for producing a metal oxide catalyst represented by thefollowing composition formula, comprising the following step (1), step(2), step (3) and step (4): Step (1): grinding metal A to a fineparticle dispersion in the presence of water without any ofMo⁶⁺compounds and V⁵⁺compounds to obtain an aqueous dispersion orgrinding metal A to a fine particle dispersion in the presence of anorganic solvent without any of Mo⁶⁺compounds and V⁵⁺compounds to obtainan organic solvent dispersion; Step (2): adding a Mo⁶⁺compound and aV⁵⁺compound to said aqueous dispersion obtained in step (1) and heatingto obtain a reaction liquid, or in the case where an organic solventdispersion has been obtained in the step (1), substituting water for theorganic solvent to obtain an aqueous dispersion and then adding aMo⁶⁺compound and a V⁵⁺compound to the aqueous dispersion and heating toobtain a reaction liquid; Step (3): adding metal B to the reactionliquid obtained in the step (2) to obtain a mixed liquid; and Step (4):evaporating to dryness and calcining the mixed liquid obtained in step(3) to obtain the composition formula:MoV_(i)A_(j)B_(k)O_(y)   Composition formula: wherein A is Te or Sb; Bis at least one element selected from the group consisting of Nb, Ta, W,Ti, Zr, Re, Fe, Ni, Co, Sn, Tl, Cu, rare earth elements, and alkalimetal elements; i and j are each from 0.01 to 1.5, and j/i is from 0.3to 1.0; k is from 0.001 to 3.0; and y is the number to be determined bythe oxidation state of other elements.
 2. The process for producing ametal oxide catalyst according to claim 1, wherein hydrogen peroxide isused in addition to water or the organic solvent.
 3. The process forproducing a metal oxide catalyst according to claim 1, wherein the fineparticle dispersion of the metal A after grinding has a mode size of notmore than 20 μm.
 4. A process for producing a metal oxide catalystrepresented by the following composition formula, comprising thefollowing step (1), step (2), step (3) and step (4): Step (1): grindingmetal A to a fine particle dispersion in the presence of water withoutany of Mo⁶⁺compounds and V⁵⁺compounds to obtain an aqueous dispersion orgrinding metal A to a fine particle dispersion in the presence of anorganic solvent without any of Mo⁶⁺compounds and V⁵⁺compounds to obtainan organic solvent dispersion; Step (2): adding a Mo⁶⁺compound and aV⁵⁺compound to said aqueous dispersion obtained in step (1) and heatingat 60° C. or higher for at least 10 minutes to obtain a reaction liquid,or in the case where an organic solvent dispersion has been obtained inthe step (1), substituting water for the organic solvent to obtain anaqueous dispersion and then adding a Mo⁶⁺compound and a V⁵⁺compound tothe aqueous dispersion and heating at 60° C. or higher for at least 10minutes to obtain a reaction liquid; Step (3): adding metal B thereaction liquid obtained in the step (2) to obtain a mixed liquid; andStep (4): evaporating to dryness and calcining the mixed liquid obtainedin step (3) to obtain the composition formula:MoV_(i)A_(j)B_(k)O_(y)  Composition formula: wherein A is Te or Sb; B isat least one element selected from the group consisting of Nb, Ta, W,Ti, Zr, Re, Fe, Ni, Co, Sn, Tl, Cu, rare earth elements, and alkalimetal elements; i and j are each from 0.01 to 1.5, and j/i is from0.3 to1.0; k is from 0.001 to 3.0; and yis the number to be determined by theoxidation state of other elements.
 5. The process for producing a metaloxide catalyst according to claim 4, wherein in step (1), hydrogenperoxide is used in addition to water or the organic solvent.
 6. Theprocess for producing a metal oxide catalyst according to claim 4,wherein in step (2), the fine particle dispersion of the metal A aftergrinding has a mode size of not more than 20 μm.
 7. A process forproducing acrylic acid, by the vapor phase catalytic oxidation ofpropane in the presence of the metal oxide catalyst as produced by theprocess according to any one of claims 2 to
 6. 8. A process forproducing acrylonitrile, by subjecting propane to ammoxidation in thepresence of the metal oxide catalyst as produced by the processaccording to any one of claims 2 to 6.